"I have neither the scholar's melancholy, which is emulation; nor the musician's, which is fantastical; nor the courtier's, which is proud; nor the soldier's, which is ambitious; nor the lawyer's, which is politic; nor the lady's, which is nice; nor the lover's, which is all these: but it is a melancholy of mine own, compounded of many simples, extracted from many objects, and indeed the sundry contemplation of my travels, in which my often rumination wraps me in a most humorous sadness."
Jacques, As You Like It
Most psychiatrists can't go a week without hearing the "guinea pig" comment from a patient alarmed by the all-too apparent imprecision of the enterprise. Problem is, it would be bad enough if treatment were up in the air; the reality is that diagnosis itself is often in flux. Two links--Mitchell Newmark, M.D. at Shrink Rap and Joe Westermeyer, M.D. in the green journal--illustrate nicely the yawning gulf between theory and practice when it comes to the art of the shrink.
Patients (and insurance companies) often crave DSM-type diagnosis for the sake of clarity, but such categories often do not usefully guide treatment. Both psychotherapeutic and biological interventions, strangely, can be both more general and more idiosyncratic than by-the-book diagnoses would suggest. After all, many of the most basic psychotherapeutic stances--Rogerian acceptance and cognitive reframing just to name two--apply across numerous diagnoses. The same may be true of medications--"antidepressants" are used to treat not only depression, but multiple anxiety disorders as well as eating disorders.
In this sense, two seemingly contradictory propositions may be said to be true: every case of depression is alike, and no two cases of depression are alike. The former may as well be the case when it comes to biological treatment, or rather, it is merely the case that depression exists on a spectrum of severity which dictates the aggressiveness (but not the basic type) of intervention. But it is just as true that when it comes to the fine-tuned approach to the patient (including, but not limited to, formal psychotherapy), myriad developmental and personal variables guide treatment far more than DSM diagnosis. Another way of putting this is that despite decades of attempts to make the DSM more specific, individuals within a category (whether schizophrenia or borderline personality disorder) are still more different than they are similar.
I think of evaluation and treatment as situated among three axes: severity, symptoms, and idiosyncratic history. The most basic question is: how impaired is the individual, and what extremity of intervention is called for? The first issue, whether evaluation or treatment is required at all, has already been answered, by the patient or someone close to him/her, by the time the clinician is on the scene. The second issue is whether biological intervention is likely to be helpful. In select cases, the third issue is whether inpatient or residential treatment is indicated.
Individuals are driven to treatment by symptoms, and once it is decided, if it is decided, that biological intervention is appropriate, it is shaped by symptoms more than by diagnoses. Yes, there are a few major categories helpfully kept in mind--primary psychotic disorder, depression/anxiety, bipolarity, substance abuse, and ADHD (or other cognitive impairments)--but those suffice for general formulation so far as biological treatment is concerned. When it comes to general and psychotherapeutic approaches, the unique idiosyncrasy of the patient is the chief guide of treatment.
As Dr. Newmark points out in his post, psychiatry remains profoundly different from the rest of medicine, where diagnosis is everything, in this respect. If a patient presents with chest pain, it is supremely important to know whether it is due to a heart attack, aortic dissection, bronchitis, pulmonary embolus, gastroesophageal reflux, or costochondritis, because each of these calls for clearly distinct treatments. Psychiatry is not like that. Deciding whether a person's diagnosis is depression, bipolar disorder, or schizophrenia will suggest moderate differences in treatment, but the latter will derive more from specific symptoms and personal background. This goes to show that psychiatry remains far more art (or "art") than science. The research-powers that be have yet to persuade the practitioner otherwise.